Synthesis And Properties Of Rare Earth Porphyrin Complexes

Porphyrin and its derivatives are a kind of biological macromolecules with special significance and closely related to life sciences.The porphyrin and metalloporphyrin compounds widely existed in nature mainly exist in the forming of chlorophyll and hemoglobin,vitamin B₁₂,etc.Rare earth metals have been extensively studied compared to other metals due to their special fluorescent properties.In this paper,Sm³⁺,Er³⁺,Yb³⁺,Gd³⁺,Pr³⁺,Nd³⁺were used as the central metal ions to react with different porphyrin ligands and organic carboxylic acid-assisted ligands to obtain rare earth porphyrin complexes.The obtained rare earth porphyrin complexes were characterized and their composition and structure were analyzed.In this study,we used two kinds of porphyrin compounds:TSPP is a water-soluble porphyrin compound,TCPP and TPyP are fat-soluble porphyrin compounds.These three kinds of porphyrin derivative ligands were regulated by hydrothermal method and solvothermal method with rare earth metal salts such as Sm³⁺,Er³⁺,Yb³⁺,Gd³⁺,Pr³⁺,Nd³⁺respectively.Eighteen rare earth porphyrin complexes were successfully synthesized at different reaction temperatures,solvents and pH values.Elemental analysis,XRD,infrared spectroscopy,ultraviolet spectroscopy and TGA were carried out for these complexes.The results of characterization confirmed that the porphyrin derivatives and rare earth metal ions formed structural formulas of[Me?NO₃?₃?TSPP?]·2H₂O?complexes 1-6?,[Me?NO₃?₃?TCPP?]·nH₂O?complexes 7,8,9,10,n=1;complexes 11,12,n=2?and[Me?NO₃?₃?TPyP?]·nH₂O?complexes 13,15,n=3;complex 14,n=2;complexes 16,17,18,n=1?(Me=Sm³⁺,Er³⁺,Yb³⁺,Gd³⁺,Pr³⁺,Nd³⁺).XRD measurements show that complexes1-6 belong to heterogeneous isomorphic complexes.Among them,nitrate not only participates in coordination?monodentated coordination?,but also plays an important role in charge balance of complexes.The ratio of three porphyrin derivative ligands to metal ions is 1:1,which also proves that porphyrin has strong macrocyclic chelating effect,and its steric hindrance determines the structure of these complexes.At the same time,due to the different substituents on porphyrin macrocycles,the structural stability of the complexes varies slightly.During the whole thermal decomposition process,the substituents of larger groups?benzsulfonic group and benzyl cyanide group?present multistage decomposition of ligands,while the substituents of smaller groups?pyridyl group?lose all organic ligands at certain temperature in the process of thermal decomposition.All the complexes were eventually decomposed into rare earth oxides and rare earth nitrides.While using a single porphyrin derivative ligand for the preparation and structure of rare earth porphyrin complexes,we also applied two different ancillary ligands:TPA and PBC,coordinated with TPyP and rare earth metal ion Pr³⁺,successfully constructed two novel metal organic materials,namely:a complex with a two-dimensional layered structure[Pr?TPA?₃?DMF??H₂O?]?19?,and zero-dimensional[Pr?PBC??NO₃?₂?H₂O?₂]·?NO₃?·2H₂O?20?.Complexes 19 and 20 belong to the triclinic system and the space group is P-1.In complex 19,Pr?III?ions exhibit an octcoordinated dodecahedral spatial structure.The oxygen atoms of carboxylic acid of ligand TPA are coordinated by bidentated chelation??²?₁?²?and tridentated??²?₂?³?modes,respectively.Due to the unique coordination mode of carboxyl group,the complex form a one-dimensional chain structure along the a-axis containing the secondary structure units of binuclear Pr?III?.Because of the ligand bidentated chelation between adjacent chains,the complex is extended to a two-dimensional layer structure in the ab plane.Since the existence of coordination water,the two-dimensional layer is extended to a three-dimensional network structure through the hydrogen bond between water and carboxyl oxygen.In complex 20,the ligand PBC was bonded by bidentate chelation??²?₁?²?,and nitrate was bonded by bidentate chelation??²?₁?²?and monodentate bridging??¹?₁?¹?,respectively.